Our objective is to develop ultrasound pulse-Doppler equipment capable of imaging blood flow in aorto-coronary artery bypass grafts. Equipment we will use is the infinite-gate pulse-Doppler adapted to imaging flow in the anterior mediastinum. This instrument uses charge-coupled cancellers to eliminate fixed structures. The ability of the system to measure absolute flow velocities or volume flows is being assessed in vitro and using an animal model. Preliminary studies of volunteers are being conducted to devise appropriate scanning hardware and techniques. Comparisons between this new technique and angiography will be made in a series of patients studied during routine follow-up examinations after surgery. We will also assess the utility of the system in following flow changes in the immediate postoperative period and subsequently using the volumetric flow measured in the operating room as a baseline reference. If the work on the grafts is sufficiently promising, we will determine the feasibility of detecting flow in the natural coronary arteries with this, or a modified, system.